Method of manufacturing apparatus for harvesting and storing piezoelectric energy

ABSTRACT

A method of manufacturing an apparatus for harvesting and storing piezoelectric energy includes forming a groove at a side on a substrate. The method further includes embedding and planarizing a polymer in the groove, forming a piezoelectric energy harvesting device, which converts and stores an external vibration into electric energy, onto the substrate, and forming a piezoelectric MEMS cantilever by forming a hole at a side of the piezoelectric energy harvesting device and by removing the polymer in the groove through the hole.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a division of application Ser. No. 13/595,070, filed Aug. 27,2012. Furthermore, this application is based on and claims priority fromKorean Patent Application No. 10-2011-0086839, filed on Aug. 30, 2011,with the Korean Intellectual Property Office. The disclosures of theseprior applications are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to an apparatus for harvesting andstoring piezoelectric energy, and more particularly, to an apparatus forharvesting and storing piezoelectric energy that can improve output bysetting the resonance frequency of a piezoelectric energy harvestingdevice to the frequency of ambient vibrations, and store power in astorage device, and a manufacturing method thereof.

BACKGROUND

A piezoelectric energy harvesting device (hereafter, referred to as a‘PEH’ device) generates the largest electric energy at the resonancefrequency due to amplification of displacement occurring when theresonance frequency of the PEH device and the frequency of ambientvibrations meet each other.

The voltage generated from the PEH device is outputted in an AC(Alternating Current) type. A rectifier is used to convert the ACvoltage into DC voltage. The rectifier is composed of four or twodiodes, in a full-bridge type or a half-bridge type. A filteringcapacitor reducing ripple of the DC voltage is connected to the rear endof the rectifier.

The output DC voltage of the filtering capacitor is used to drive an ICsuch as a memory, and MCU and RF transmitting/receiving devices.However, the electric energy obtained from small vibrations in anambient environment is very small in magnitude, so the electric energyis not enough to drive an IC. Accordingly, methods of using storedpower, if needed, by charging a storage device, such as a supercapacitor, a secondary battery and a thin film battery, have beenstudied.

The electronic devices used at present in wireless sensor nodes moreautomatically operate by actively performing the functions or passivelysensing or collecting information. For this configuration, amicro-energy supply device that can continuously supply power isrequired. Although batteries can perform this function, the amount ofavailable energy decreases as time passes due to a limit in the storagecapacity, and consequently, it becomes impossible to supply power to awireless sensor node.

SUMMARY

The present disclosure has been made in an effort to provide amicro-apparatus for harvesting and storing piezoelectric energy that canreduce an electrical loss by setting the resonance frequency of apiezoelectric energy harvesting device to the frequency of ambientvibrations, and can store power in a storage device such as a supercapacitor, a secondary battery, and a thin film battery, and amanufacturing method thereof.

The present disclosure also has been made in an effort to provide anapparatus for harvesting/storing piezoelectric energy of which themanufacturing cost can be reduced by simplifying the manufacturingprocess, and a manufacturing method thereof.

An exemplary embodiment of the present disclosure provides an apparatusfor harvesting/storing piezoelectric energy, including: a substratehaving a groove at a side thereon; a piezoelectric MEMS cantileverhaving an end fixed to the substrate and the other end floating abovethe groove, and configured to convert and store an external vibrationinto electric energy; and a mass formed at one end of the piezoelectricMEMS cantilever and configured to apply a vibration.

Another exemplary embodiment of the present disclosure provides a methodof manufacturing an apparatus for harvesting/storing piezoelectricenergy, including: forming a groove at a side on a substrate; embeddingand planarizing a polymer in the groove; forming a piezoelectric energyharvesting device, which converts and stores an external vibration intoelectric energy, onto the substrate; and forming a piezoelectric MEMScantilever by forming a hole at a side of the piezoelectric energyharvesting device and by removing the polymer in the groove through thehole.

As described above, according to the present disclosure, it is possibleto use an apparatus for harvesting/storing piezoelectric energy thatconverts and stores peripheral vibrations into electric energy as powersources of the devices constituting a wireless sensor network that isself-chargeable and has integrity.

According to the present disclosure, it is possible to implement amicro-self-chargeable power module and an implant type of capsule byproviding an apparatus for harvesting/storing piezoelectric energy in anarray type.

According to the present disclosure, it is possible to achieve massproduction because the manufacturing process is simple, and to integratethe apparatus in a sensor using a MEMS process, by providing anapparatus for harvesting/storing piezoelectric energy in an array typeand a manufacturing method thereof.

According to the present disclosure, it is possible to increaseperformance of collecting energy because the gaps between devices arevery small, by providing an apparatus for harvesting/storingpiezoelectric energy in an array type and a manufacturing methodthereof.

The foregoing summary is illustrative only and is not intended to be inany way limiting. In addition to the illustrative aspects, embodiments,and features described above, further aspects, embodiments, and featureswill become apparent by reference to the drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are a plan view and a cross-sectional view, respectively,of an apparatus for harvesting/storing piezoelectric energy according toan exemplary embodiment of the present disclosure.

FIG. 3 is a cross-sectional view of a thin film battery according to anexemplary embodiment of the present disclosure.

FIGS. 4A to 4D are process flowchart illustrating a method ofmanufacturing an apparatus for harvesting/storing piezoelectric energyaccording to an exemplary embodiment of the present disclosure.

FIG. 5 is a circuit diagram of an apparatus for harvesting/storingpiezoelectric energy according to an exemplary embodiment of the presentdisclosure.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawing, which form a part hereof. The illustrativeembodiments described in the detailed description, drawing, and claimsare not meant to be limiting. Other embodiments may be utilized, andother changes may be made, without departing from the spirit or scope ofthe subject matter presented here.

Hereinafter, an exemplary embodiment of the present disclosure will bedescribed in detail with reference to the accompanying drawings. Indescribing the present disclosure, well-known functions or constructionswill not be described in detail since they may unnecessarily obscure theunderstanding of the present disclosure.

In general, a piezoelectric energy harvesting device (hereafter,referred to as a ‘PEH’ device) falls into a piezoelectric monomorph PEHdevice composed of a single piezoelectric layer generating electricoutput by using pressure or vibration and a non-piezoelectric layer (forexample, Si and Al) reinforcing the brittleness of the piezoelectriclayer and a piezoelectric bimorph PEH device with piezoelectric layerstacked at both sides of a non-piezoelectric layer. There is amultilayer PEH device implemented by stacking a plurality ofpiezoelectric layers, instead of stacking two piezoelectric layers.

An apparatus for harvesting/storing piezoelectric energy and a method ofmanufacturing the apparatus are described by exemplifying apiezoelectric monomorph PEH device.

FIGS. 1 and 2 are a plan view and a cross-sectional view, respectively,of an apparatus for harvesting/storing piezoelectric energy according toan exemplary embodiment of the present disclosure.

Referring to FIGS. 1 and 2, an apparatus for harvesting/storingpiezoelectric energy according to an exemplary embodiment of the presentdisclosure includes a substrate 110, a piezoelectric MEMS (Micro ElectroMechanical Systems) cantilever 120, and a tip mass 130.

The substrate 110 has a groove 112 at a side thereon and may be a SOI(Silicon-on Insulator) wafer. The SOI wafer is implemented by insertingan Si layer having a thickness of 20 μm and an SiO₂ layer having athickness of 1 μm between Si. SiO₂ or Si₃N₄ may be deposited on thesubstrate 110 according to an exemplary embodiment of the presentdisclosure to prevent diffusion of a piezoelectric material to thesubstrate 110 in deposition of a piezoelectric layer 125 and an electricshort and remove residual stress of a multilayer structure.

The piezoelectric MEMS cantilever 120 has one end fixed to the substrateand the other end floating above the groove 112, and converts and storesan external vibration into electric energy. For this configuration, thepiezoelectric MEMS cantilever 120 includes a capacitor 121, a firstelectrode 122, a thin film battery 123, a second electrode 124, apiezoelectric layer 125, and a third electrode 126.

The capacitor 121 reduces ripple of the voltage outputted from arectifier (not illustrated). The capacitor 121, as illustrated in FIG.2, may be manufactured in advance in the apparatus forharvesting/storing piezoelectric energy or may be connected in a chipcapacitor type at the outside.

The first electrode 122 has high electric conductivity and thermalstability at a high temperature and contains Pt/Ti to increase anadhesive property for a lower layer.

The thin film battery 123, a storage device storing electric energy, isformed on the first electrode 122 and stores the electric energyconverted by the piezoelectric layer 125. For this configuration, thethin film battery 123 may be composed of two current collectors, twoelectrodes, and an solid electrolyte therebetween, which is described indetail with reference to FIG. 3.

A second electrode 124 is formed on the thin film battery 123. Thesecond electrode 124 has high electric conductivity and thermalstability at a high temperature and contains Pt/Ti to increase anadhesive property to a lower layer.

A piezoelectric layer 125 is formed on the second electrode 124 andconverts an external vibration into electric energy. The piezoelectriclayer 125 may contain PZT, PMN-PT, PZN-PT, PMN-PZT, MFC (Micro-fiberComposite), ZnO, and AlN and may be achieved by multi-coating until adesired thickness is obtained.

A third electrode 126 is formed on the piezoelectric layer 125, has highelectric conductivity, and contains Pt to have thermal stability at ahigh temperature.

The tip mass is positioned at one end of the third electrode 126 andapplies a vibration to the piezoelectric MEMS cantilever 120.

As described above, it is possible to provide a micro-apparatus forharvesting/storing piezoelectric energy by providing an apparatus forharvesting/storing piezoelectric energy in which a PEH device and astorage device are integrated on the same substrate, in an exemplaryembodiment of the present disclosure.

FIG. 3 is a cross-sectional view of a thin film battery according to anexemplary embodiment of the present disclosure.

Referring to FIG. 3, the thin film battery 123 according to an exemplaryembodiment of the present disclosure includes a substrate 300, a firstcurrent collecting layer 310, a first electrode 320, an electrolytelayer 330, a second electrode 340, and a second current collecting layer350.

The substrate 300 may be made of Si, glass, ceramic, metal, plastic, anda polymer.

The first current collecting layer 310 is formed on the substrate 300and contains Pt/Cr.

The first electrode 320 is formed on the first current collecting layer310 and contains LiCoO₂. The first electrode 320 may be a cathodeelectrode or an anode electrode.

The electrolyte layer 330 is formed on the substrate 300 including thefirst electrode 320 and may be made of a lithium mixture.

The second electrode 340 is formed on the electrolyte layer 330 andcontains SnO. The second electrode 340 may be an anode electrode or acathode electrode with a polarity opposite to that of the firstelectrode 320.

The second current collecting layer 350 is formed on the secondelectrode 340 and contains Pt.

The thin film battery 123 according to an exemplary embodiment of thepresent disclosure may further include a protective layer (notillustrated) covering the entire thin film battery 123 to preventdiffusion of the lithium in the electrolyte layer 330.

FIGS. 4A to 4D are process flowchart illustrating a method ofmanufacturing an apparatus for harvesting/storing piezoelectric energyaccording to an exemplary embodiment of the present disclosure.

Referring to FIG. 4A, the groove 112 is formed at a side on thesubstrate 110, which may be a Si substrate or a SOI substrate. Indetail, the groove 112 is formed by forming a rectangular photoresistpattern at the position where the piezoelectric MEMS cantilever 120 isformed, and then performing RIE (Reactive Ion Etching).

Referring to FIG. 4B, the groove 112 is filled with a polymer 113 suchas PMMA or SU8 and then the polymer 113 is planarized by CMP (ChemicalMechanical Polishing). The polymer 113 prevents side etching by beingprovided with higher selection ratio than silicon in isotropic dryetching using SF₆ or XeF₂, which is described below.

Referring to FIG. 4C, a PEH device is formed by sequentially stackingthe capacitor 121, the first electrode 122, the thin film battery 123,the second electrode 124, the piezoelectric layer 125, and the thirdelectrode 126, on the substrate 110. The first electrode 122 and thesecond electrode 124 are formed by sputtering with Pt/Ti. Thepiezoelectric layer 125 is formed by multi-coating with a piezoelectricmaterial such as PZT, PMN-PT, PZN-PT, PMN-PZT, MFC (Micro-fiberComposite), ZnO, and AlN and until a desired thickness is obtained. Thethird electrode 126 is formed by sputtering with Pt.

Meanwhile, a method of manufacturing the thin film battery 123 accordingto an exemplary embodiment of the present disclosure is described belowwith reference to FIG. 3.

The first current collecting layer 310 is formed by depositing Pt/Cronto the substrate 300 and the first electrode 320 is formed bydepositing LiCoO₂ onto the first current correcting layer 310.

Subsequently, the electrolyte layer 330 is formed by depositing alithium mixture onto the substrate 300 including the first electrode320.

Finally, the second electrode 340 is formed by depositing SnO onto theelectrolyte layer 330 and the second current collecting layer 350 isformed by depositing Pt onto the second electrode 340.

A protective layer (not illustrated) covering the entire thin filmbattery 123 may be further formed to prevent diffusion of the lithium inthe electrolyte layer 330.

Referring to FIG. 4D, a hole 120 a is formed at a side of the PEH deviceby isotropic dry etching using XeF₂ or SF₆ and the piezoelectric MEMScantilever 120 is formed by removing the polymer 113 in the groove 112through the hole 120 a. The mass 127 is formed in this process, using aphotoresist pattern.

FIG. 5 is a circuit diagram of an apparatus for harvesting/storingpiezoelectric energy according to an exemplary embodiment of the presentdisclosure.

As illustrated in FIG. 5, the apparatus for harvesting/storingpiezoelectric energy according to an exemplary embodiment of the presentdisclosure includes a PEH device 510, a rectifier 520, a capacitor 530,a DC-DC power converter 540, and a storage device 550.

The PEH device 510 converts an external vibration into electric energyand outputs an AC voltage.

The rectifier 520 converts the AC voltage generated from the PEH device510 into a DC voltage. The rectifier 520 may be manufactured in advancein the apparatus for harvesting/storing piezoelectric energy or may beconnected in an IC type at the outside.

The capacitor 530 reduces ripple of the DC voltage outputted from therectifier 520. The capacitor 530, as illustrated in FIG. 2, may bemanufactured in advance in the apparatus for harvesting/storingpiezoelectric energy or may be connected in an IC type at the outside.

The DC-DC power converter 540 converts the DC voltage outputted from thecapacitor 530 to a voltage suitable to be stored in the storage device550. The DC-DC power converter 540 may also be manufactured in advancein the apparatus for harvesting/storing piezoelectric energy or may beconnected in an IC type at the outside.

The storage device 550 stores the voltage outputted from the DC-DC powerconverter 540. Although the exemplary embodiment of the presentdisclosure exemplifies a thin film battery as the storage device 550,the storage device 550 may be a super capacitor and a secondary battery.

Further, although the exemplary embodiment of the present disclosureexemplifies a single PEH device and a single thin film battery for theconvenience of description, the present disclosure is not limitedthereto, and a plurality of PEH devices may be arranged in an array typeor a plurality of thin film batteries may be connected with a PEH devicein parallel or in series in order to increase the output voltage of theapparatus for harvesting/storing piezoelectric energy.

From the foregoing, it will be appreciated that various embodiments ofthe present disclosure have been described herein for purposes ofillustration, and that various modifications may be made withoutdeparting from the scope and spirit of the present disclosure.Accordingly, the various embodiments disclosed herein are not intendedto be limiting, with the true scope and spirit being indicated by thefollowing claims.

What is claimed is:
 1. A method of manufacturing an apparatus forharvesting/storing piezoelectric energy, comprising: forming a groove ata side on a substrate; embedding and planarizing a polymer in thegroove; forming a piezoelectric energy harvesting device, which convertsand stores an external vibration into electric energy, onto thesubstrate; and forming a piezoelectric MEMS cantilever by forming a holeat a side of the piezoelectric energy harvesting device and by removingthe polymer in the groove through the hole, wherein the forming of thepiezoelectric energy harvesting device includes: forming a capacitor;forming a first electrode onto the capacitor; forming a thin filmbattery onto the first electrode; forming a second electrode onto thethin film battery; forming a piezoelectric layer onto the secondelectrode; and forming a third electrode onto the piezoelectric layer.2. The method of claim 1, wherein the polymer is PMMA or a SU8 polymer.3. The method of claim 1, wherein the forming of the groove throughreactive ion etching.
 4. The method of claim 1, wherein the forming ofthe piezoelectric MEMS cantilever forms the hole at the side of thepiezoelectric energy harvesting device through isotropic dry etchingusing XeF₂ or SF₆, and removes the polymer in the groove through thehole.
 5. The method of claim 1, wherein the forming of the piezoelectricMEMS cantilever forms a mass at one end of the piezoelectric MEMScantilever, simultaneously with forming the piezoelectric MEMScantilever.
 6. The method of claim 1, wherein the forming of the thinfilm battery includes: forming a first current collecting layer; forminga first electrode on the first current collecting layer; forming anelectrolyte layer onto another substrate including the first electrode;forming a second electrode onto the electrolyte layer; and forming asecond current collecting layer onto the second electrode.
 7. The methodof claim 6, wherein the forming of the thin film battery furtherincludes forming a protective layer covering the entire thin filmbattery.